This invention relates to sending electrical signals along a transmission line to trigger a receiver at a time independent of the relative positions of the signal source and the receiver along the line.
It is often desirable to simultaneously trigger a number of receivers spaced along a transmission line. But, because of signal propagation delay times, a signal sent along the line from one end will reach the receivers at different times. In a high speed digital board tester, for example, multiple units are simultaneously tested and there must be precise synchronism of driver transitions applied to each of the units under test, as such driver transitions must change at specified times. Similarly, detection windows must be accurately synchronized as signals coming from the units under test to the tester detectors are expected to be valid for precise time intervals. Such testers operate at high speeds, up to 10 megahertz or more, and the signal transmission time along the back plane may be several nanoseconds as such back planes may be five feet or more in length. Signal propagation delay times in such systems are significant where signal synchronization tolerances in the order of .+-.5 nanoseconds or less are involved.